The present invention relates to the preparation of 3,5-dichloro-2,4,6-trifluoropyridine from pentachloropyridine by halogen exchange.
The preparation of 3,5-dichloro-2,4,6-trifluoropyridine by processes involving the reaction of pentachloropyridine and potassium fluoride at temperatures of about 200.degree. C. and higher is known. Dipolar, aprotic solvents have been utilized in these processes (U.S. Pat. No. 3,303,107). The process has also been taught to proceed satisfactorily at temperatures as low as 160.degree. C. in a dipolar, aprotic solvent if an initiator such as ethylene glycol (British Pat. No. 1,306,517) or about 0.2 to about 2 percent water (British Pat. No. 1,256,082) is added. These processes all suffer because they provide only moderately high yields of the desired product, usually mixed with tarry degradation products, and generally require an excess of potassium fluoride to be employed for good results.
Improved processes for the production of 3,5-dichloro-2,4,6-trifluoropyridine are desirable as this compound is employed as an intermediate for the production of herbicides, such as 4-hydroxy-3,5-dichloro-2, 6-difluoropyridine and 4-amino-3,5-dichloro-6-fluoro-2-pyridinyloxyacetic acid, and is useful among other things for fixing dyes to fabric.